The present invention relates to a method of detecting a train in a block section using a track circuit, and particularly to a train detecting method which is capable of maintaining safety even in the event of a failure in a signal transmission path of the track circuit.
A conventional railway system employs a method which uses a track as part of a signal transmission path to detect the existence of a train in a block section. In such a method, the track is electrically divided into plural sections, each having a predetermined length. Such a section forms a part of an electric circuit, which is commonly referred to as a track circuit. At respective ends of each track circuit, there are arranged transmitter/receiver devices, one of which transmits a signal for detecting a train continuously or at a constant time interval and the other of which receives the transmitted signal.
If a train does not exist in the section formed by a track circuit, a signal transmitted by a unit on the transmitting side is able to reach the unit on the receiving side. If, however, a train exists in the section formed by the track circuit, a signal transmitted by a unit on the transmitting side does not reach the unit on the receiving side, because the pair of rails which form the track circuit are short-circuited by the wheels of the train. Thereby, the existence of a train in the section can be detected.
In detecting the existence of a train, a high reliability is required, because a control device on the ground (a wayside controller) utilizes a train detecting signal generated as described above to locate the train and to operate traffic signals for the train. Particularly, for the purpose of securing adequate safety in the train service, it is absolutely essential to avoid possibility that, although a train actually exists within a certain section forming a track circuit and therefore the pair of rails which form the track are short-circuited, a signal indicating no train in the section of the track circuit is erroneously transmitted, possibly due to a failure in a transmitter/receiver device, for example.
Conventionally, to solve such a problem, highly reliable equipment has been used for the transmitter/receiver devices installed in every track circuit, as well as for the wayside controller. When any trouble occurs in transmitting or receiving signals, the control which is carried out is as follows: i.e., no signal is transmitted on the transmitting side, and a determination is then made as to whether no signal is received on the receiving side.
In the conventional system as mentioned above, the large number of transmitter/receiver devices must be subject to very careful maintenance. Further, an individual signal cable is used for the connection between every transmitter/receiver device and the wayside controller, in order to avoid possible misrecognition of information among the devices.
Furthermore, JP-A 6-92232 proposes that a signal, which has a different frequency for every track circuit, be used in order to avoid erroneously receiving a train detecting signal from an adjacent track circuit.
To sum up, as described above, when any trouble occurs in transmitting or receiving, the conventional system carries out control in such a manner that, if trouble occurs on the transmitting side, no signal is transmitted, and if it occurs on the receiving side, it is judged that no signal is received. To this end, highly reliable devices must be utilized for a transmitter/receiver device. As a result, the transmitter/receiver device has become complicated in its structure and therefore can not be made small in size.
Since such a device is needed for every track circuit, the total system becomes extremely high in cost. Further, in order for a transmitter/receiver device to achieve the above mentioned control, it must be sufficiently maintained and inspected. Such maintenance and inspection work is very troublesome, since the work must be done for every one of a large number of devices arranged along a wayside.
Further, while the technology disclosed in JP-A-6-92232 might have the effect to avoid erroneously receiving a train detecting signal from an adjacent track circuit, it cannot solve the problem of being high in cost, due to its complicated system construction, which is needed for maintaining the reliability of a transmitter/receiver device, nor the problem of being very troublesome in the amount of maintenance and inspection work required to assure proper operation thereof.